Investigation of toluene removal by DC discharge with MgO/NiO/Ni cathode under different operating parameters

Abstract

The degradation of toluene by DC discharge has been evaluated in a multi-wire-plate reactor with MgO/NiO/Ni (MNN) cathode and compared with a normal discharge with Ni cathode. The effects of various operating parameters, including the position distribution of wire electrodes, discharge gap, gas flow rate and toluene initial concentration have been systematically investigated. Morphological characterizations demonstrate that in addition to the normal discharge around the wire electrodes, extra discharge also occurs on the MNN cathode surface which is mainly concentrated in the vertical corresponding region of the wire electrodes and diffuses to both sides. The position distribution of two wires influences the total discharge current. It is because that it affects not only the discharge around the wire electrode, but also the discharge on MNN cathode surface. Beside, a wire–wire spacing of 25 mm in discharge reactor with MNN cathode is optimized due to a relative large discharge current. A small discharge gap between wire electrode and cathode contributes to the improvement of toluene degradation and mineralization and it is optimized of 15.3 mm. The effects of discharge power, gas flow rate and toluene initial concentration and the interactions between these parameters on toluene removal performance by discharge with MNN cathode are investigated using Box–Behnken design (BBD). The analysis of variance (ANOVA) is employed to evaluate the significance of the independent variables and their interactions. The results show that the initial concentration plays the most important role in determining the toluene removal efficiency, while discharge power is the most significant factor affecting the energy efficiency in this discharge process.